Department of Psychiatry, University of Michigan, 4250 Plymouth Road, Ann Arbor, MI 48109, United States.
Department of Psychology, University of Michigan, 530 Church Street, Ann Arbor, MI 48109, United States.
Cereb Cortex. 2024 Sep 3;34(9). doi: 10.1093/cercor/bhae352.
Paired-pulse transcranial magnetic stimulation is a valuable tool for investigating inhibitory mechanisms in motor cortex. We recently demonstrated its use in measuring cortical inhibition in visual cortex, using an approach in which participants trace the size of phosphenes elicited by stimulation to occipital cortex. Here, we investigate age-related differences in primary visual cortical inhibition and the relationship between primary visual cortical inhibition and local GABA+ in the same region, estimated using magnetic resonance spectroscopy. GABA+ was estimated in 28 young (18 to 28 years) and 47 older adults (65 to 84 years); a subset (19 young, 18 older) also completed a paired-pulse transcranial magnetic stimulation session, which assessed visual cortical inhibition. The paired-pulse transcranial magnetic stimulation measure of inhibition was significantly lower in older adults. Uncorrected GABA+ in primary visual cortex was also significantly lower in older adults, while measures of GABA+ that were corrected for the tissue composition of the magnetic resonance spectroscopy voxel were unchanged with age. Furthermore, paired-pulse transcranial magnetic stimulation-measured inhibition and magnetic resonance spectroscopy-measured tissue-corrected GABA+ were significantly positively correlated. These findings are consistent with an age-related decline in cortical inhibition in visual cortex and suggest paired-pulse transcranial magnetic stimulation effects in visual cortex are driven by GABAergic mechanisms, as has been demonstrated in motor cortex.
成对脉冲经颅磁刺激是研究运动皮层抑制机制的一种有价值的工具。我们最近证明了它在测量视觉皮层皮质抑制中的应用，使用的方法是让参与者追踪刺激枕叶皮层引起的光幻视的大小。在这里，我们研究了初级视觉皮层抑制的年龄相关性差异，以及同一区域内初级视觉皮层抑制与局部 GABA+之间的关系，使用磁共振波谱法估计 GABA+。GABA+在 28 名年轻（18 至 28 岁）和 47 名老年（65 至 84 岁）成人中进行了估计；一小部分（19 名年轻，18 名老年）还完成了一项成对脉冲经颅磁刺激测试，评估视觉皮层抑制。老年组的成对脉冲经颅磁刺激抑制测量值明显较低。初级视觉皮层的未校正 GABA+在老年组中也明显较低，而磁共振波谱仪体素组织成分校正后的 GABA+测量值则随年龄变化不变。此外，成对脉冲经颅磁刺激测量的抑制与磁共振波谱测量的组织校正 GABA+呈显著正相关。这些发现与视觉皮层皮质抑制的年龄相关性下降一致，并表明，与运动皮层中已证明的情况一样，成对脉冲经颅磁刺激对视觉皮层的影响是由 GABA 能机制驱动的。
